1. Field of the Invention
The present invention relates to a lens system for use in a camera with a range-finder and, more particularly, to a compact telephoto type lens system with improved focusing capabilities.
2. Description of the Prior Art
In the optical and photography fields, there is a constant demand to provide improved compact cameras and lens systems. Recent advances in automating numerous camera features have further complicated camera designs with regard to space and have imposed increased limitations on the accompanying lens designs.
Camera designers have attempted to take advantage of telephoto type lens designs to decrease the total length of the entire lens system, see U.S. Pat. No. 4,204,747. To decrease the total length of the lens system, a negative refractive power on the rear side of the lens system has been found favorable for reducing the telephoto ratio. This design approach has been generally limited to a telephoto lens system with a relatively narrow field angle because lens systems with wide field angles usually experience increases in aberrations with an increase in field angle.
Japanese Patent Application Laid Open No. 54-76147 discloses a relatively wide angle telephoto lens system with a rearmost lens element of a positive value. U.S. Pat. No. 2,503,789, while not directed to a telephoto lens system, is cited for its feature of focusing by shifting a rearmost negative lens group. Finally, Japanese Patent Application Laid Open No. 54-73014 has a publication date of June 6, 1980, and is cited of general interest.
Camera manufacturers are still seeking an optimum relatively wide angle lens system that can be readily and economically manufactured to provide not only a compact camera with an expected level of optical performance, but a lens system that is particularly adaptable to accommodating recent camera innovations such as auto focusing.